The invention relates to a picture display device provided with a cathode ray tube comprising a base, an electron gun and a cathode, the cathode having electric current conductors which are connected to external electronics via the base. The invention also relates to a cathode ray tube comprising an electron gun with a cathode.
A cathode ray tube for a monochrome picture display device, for example a television or a monitor, has a display screen with a phosphor layer. The cathode ray tube also comprises an electron gun which emits an electron beam during operation. This beam can be controlled by means of deflection coils which generate a given magnetic field towards a given location on the display screen.
The display screen is activated by scanning the electron beam across the screen, which beam is modulated by a video signal. This video signal ensures that the phosphor is excited in accordance with such a pattern that a picture is produced when the phosphor luminesces. When many electrons land on the pixel during the excitation time of a pixel, this pixel lights up more brightly. The video signal is applied to the cathode via electric current conductors each connected to a pin in the base. These electric current conductors are shown, for example in the electron gun depicted in FIG. 3 of U.S. Pat. No. 4,720,654.
There are many pixels per surface unit. Moreover, the pixels are excited one after the other within a very short time. The viewer thereby experiences a moving image at a normal viewing distance.
In a color display device, for example a color television or a color monitor, each pixel has three phosphor elements each luminescing in a different primary color. As it were, there are three uniform, regular patterns on the display screen, each pattern having a different luminescence color. Instead of one electron beam, three electron beams from three different cathodes in the color electron gun are scanned across the screen during operation. Each of these three beams excites the pixels of a given luminescence color. Since the phosphor elements of a pixel are located close together, the viewer experiences them as a single element instead of separate elements. The color which is experienced is a mixed color of the three elements. By exciting each element at a given intensity, the viewer experiences a given color. For example, if the red element and the blue element are fully excited and the green element is partly excited, the viewer will experience the mixed color of purple. Similarly as in a monochrome cathode ray tube, the pixels are located so close together that the viewer does not see them as separate pixels from a normal viewing distance. This results in a color image.
The known picture display devices have a considerable drawback in that the image is not sharp enough, notably for monitor applications.
It is, inter alia, an object of the invention to obviate the above-mentioned drawback. More particularly, it is an object of the invention to provide a picture display device in which the displayed image is sharp enough for monitor applications.